Study of rail-wheel contact problem by analytical and numerical approaches

This study presents the rail wheel contact problems under normal and tangential categories. Both analytical and numerical approaches were used for modelling, where the analytical approach assumed elliptical contact patches based on the Hertz theory. In the numerical approach, 3D finite element models were used to investigate non-elliptical contact patches. The only elastic material model was considered in the case of Hertz theory. However, in the case of finite element analysis, both elastic and elastoplastic material models were used to simulate the material's behavior under the applied load. The elastoplastic material model was used to determine the amount of stress at which the plastic deformation starts, which enables determining the rail wheel's critical load. The commercial software ABAQUS was employed for 3D modeling and contact stress analysis. The study shows maximum stress at 3 mm from the rail wheel contact surface when the maximum load of 85 kN is applied. This initiates the cracks in the subsurface and causes the portion of the rail wheel to break off in the form of spalling after a certain time.

Professor Duncan Dowson, a source of inspiration

The current paper highlights the contribution of the Dowson and Higginson work to numerical line contact elastohydrodynamic lubrication film thickness prediction and the Hamrock and Dowson contribution to the film thickness prediction in elliptical contacts. This paper shows that, even by today’s standards, both the numerical pressure and film thickness results and the curve-fitted film thickness predictions are very accurate. As for the elliptical results, the authors show that the original predictions remain surprisingly accurate for moderately elliptical contact. For very long elliptical contacts, their prediction does not tend to a line contact asymptote. This paper then concludes that the predicted pressure spikes by Dowson, Higginson, and Hamrock are correct in shape and amplitude, at least near pure rolling conditions.

Fretting Wear Observation of Flat Contacts

With the instrumentality of a newly developed fretting test bench for planar contacts, a state-of-the-art method of inter-mediate imaging helps to understand fretting wear mechanisms of different materials and lubricants. The test bench uses application like planar surfaces unlike the usual point or elliptical contact in model testing (with the tribological test chain). Applications considered prone to fretting wear have large planar contacts – like bearing seats and shaft hub connections – and contact pressures normally perceiv ed as low or uncritical. This article examines a method to evaluate a targeted observation of the surfaces. The method uses a movable upper sample to open the contact and to document an interim status of the test by image recording. Among other things, this is to obtain time-lapse recordings of the progressive wear and tear. Just opening the contact can already influence the tribological system and the result of a test. It is shown whether and how this opening process has an impact on tests with continuous contact.

A Theoretical Model for the Normal Contact Force of Two Elastoplastic Ellipsoidal Bodies

To model the mechanical behavior of granular materials, a reliable description of the material properties is indispensable. Individual grains are usually not perfectly spherical. In batteries, for instance, lithium nickel manganese cobalt oxide (NMC) is a frequently used material, consisting out of particles with possibly ellipsoidal like shapes. As particles may plastically deform under increasing stresses, the paper presents a theoretical model for the normal contact force of elastoplastic ellipsoidal bodies for the use in the context of mechanical discrete element method (DEM). The model can be considered as extension of the elastic, elastic-plastic, fully plastic Thornton model by using a more general description to incorporate elliptical contact areas. The focus is on a normal contact force description as continuous function of time for all regimes, elastic, elastoplastic, and fully plastic loading, as well as unloading from elastoplastic loading, while the evolution of the plastic contact area is not considered here. All underlying formulae to describe the force-displacement relationship for the static contact problem are derived, partly based on finite element analysis (FEA). To verify the new model, FEAs are performed and their results compared with the model predictions.

Acoustic response of high-speed deep groove ball bearing by modifying the internal geometry

In this paper, a mathematical model to predict acoustic responses of high-speed bearing has been developed and demonstrated in an application of Induction motors. Effect on the acoustic behaviour of bearing has studied by modifying the internal geometry, such as the number of rotating elements, curvature ratio, rotating speed with the oval shape of the track raceway due to pre-operational damage. The mathematical model predicts the contact stress, elliptical contact area, noise level dB and Frequencies of waviness pattern. High-speed bearing is tested at four different speeds to monitor acoustic behaviour. This drive end bearing undergoes different rotational speeds; however, the author has simulated the results at a majorly driven constant speed. The author has incorporated application-level testing at the customized test rig. The mathematical model has simulated using coupled governing equations with the help of the Ranga-Kutta method. The simulation and experimental results presented in this paper in the form of a waterfall diagram, FFT spectrum and colour pressure plots. Acoustic characteristics during measurements of the rolling bearing have shown systematically to correlate the mathematical model with an experimental result. Results indicate the remarkable influence of raceway nonconformities of bearing on the noise level. The novelty of research study is to estimate the amplitude of noise level due to waviness generated on rings of bearing after pre-operation damage which is the realistic scenario that occurred after a complaint recorded by the motor manufacturer. The authors believe that this technique enables the bearing designer to choose the appropriate diametric ratio of the ball and track curvature for elliptical contact stress as well as acoustic level. This method is developed specifically for an application of drive-end position ball bearing. Practical use of this method is to determine the Noise level of an electric motor (up to 60 kW capacities) due to improper handling and inappropriate installation of bearing which cause inherent waviness on components.

Numerical Procedure for Non-Hertzian Wheel-Rail Contact Model Integrated in Quasi-Steady Railway Vehicle Motion Solver

Although the Hertzian contact theory is widely utilized in railway vehicle simulations with new wheel and rail profiles, the Hertzian contact assumptions would lead to inaccurate contact prediction for severely worn wheel and rail profiles due to their geometric conformity, causing non-elliptical contact shapes as well as pressure distribution. For this reason, various non-Hertzian contact models have been studied for use in vehicle dynamics simulations. Among others, a method proposed by Piotrowski and Kik has gained acceptance in predicting non-elliptical wheel-rail contact for vehicle dynamics simulations. Despite the elegant formulation and its accuracy, detailed online geometric calculation for non-elliptical contact shape is required for all the contact patches at every iteration, along with iterative evaluation of the force-deflection relationship. It leads to computation burdens for use in long-distance vehicle simulations. Therefore, in this study, an off-line based numerical procedure for non-Hertzian contact model is developed and integrated in the quasi-steady railway vehicle motion solver.